Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
CDC Home

Frequently Asked Questions

What methods constitute the accuracy base for lipids and lipoproteins?

National Cholesterol Education Program (NCEP) has recommended that CDC's reference methods be used as the accuracy base for measurement of total cholesterol, HDL cholesterol, LDL cholesterol, and triglycerides. The Abell-Kendall reference method for cholesterol (the AK method) is recognized as an integral part of the National Reference System for Cholesterol. The AK method is the basis for quantification of cholesterol in the reference methods for HDL cholesterol and LDL cholesterol.

Why should my company go through the certification process?

For physicians to apply the clinical guidelines issued by the NCEP, individual laboratory measurements must be traceable to the recommended accuracy base. The certification process ensures that the method in question is traceable to the recommended accuracy base. Gaining certified status also facilitates Food and Drug Administration clearance of diagnostic products. In addition, ongoing certification assures the end users that the product is validated at all times. Many clinical laboratories rely on the diagnostic manufacturers to maintain certified methods.

What is involved in the certification process?

The participating manufacturer contacts a CRMLN laboratory about its desire to be certified and to obtain the protocol. The manufacturer and CRMLN laboratory should discuss the timeline for completion of the certification process. The participant collects samples of required specifications. An aliquot of each sample is analyzed at the participant's facility, and a second aliquot is shipped to the CRMLN lab for analysis. The participant's results are sent to the CRMLN lab for statistical method comparison. If the results meet passing criteria, CDC generates a certificate bearing the participant and the certifying CRMLN laboratory's names. The certificate is forwarded to the CRMLN lab for the director's signature before mailing to the participant. The CRMLN lab customarily notifies the participant of its pass/fail status by phone or fax before the final certificate is generated.

Can more than one instrument system or model be certified with the same set of samples?

Yes. This is cost effective and highly desirable but requires coordination within the manufacturing facility (especially if the systems are located in different locations) and with the CRMLN laboratory. Sample volume and turnaround time are important considerations with this approach.

If my company has the reference method set up in house, how can I use it to support the evaluation protocol with the CRMLN laboratory?

Comparison of the test method with the reference method should help you determine whether your routine method has an acceptable bias and hence improve your likelihood of a successful evaluation. The CRMLN laboratory has undergone a rigorous initial evaluation protocol and participates in frequent, routine monitoring of its reference methods to ensure the highest degree of confidence in the (reference) values assigned to the unknowns used in the comparison.

How long will the entire certification process take from sending samples to receiving the certificate?

As long as the CRMLN laboratory is aware that samples are arriving and can plan the analytical runs accordingly, then the entire process should take 4 - 8 weeks. The clinical laboratory certification should be completed within 4 weeks. However, this should be verified with the CRMLN laboratory you have chosen to perform the reference method analyses.

What are the certification criteria?

Parameter TC HDL LDL
r2 > 0.975
Bias at medical decision points ≤3% at 200 and 240 mg/dL ≤5% at 40 and 60 mg/dL ≤4% at 100, 130, and 160 mg/dL
Average % bias 3% ≤5% ≤4%
Average absolute % bias ≤3% ≤5% ≤4%
Among-run CV ≤3% ≤4% ≤4%
t-test of bias Not significant at α = 5%
Within-method outliers ≤1 allowed
Between-method outliers None allowed but may eliminate one sample and reanalyze the data one time
When does the certificate expire?

The certificate expires 2 years from the date of the statistical data analysis performed in the CRMLN laboratory.

Does the CRMLN have a protocol for recertification?

The CRMLN has a recertification protocol for total cholesterol (but not for HDL cholesterol or LDL cholesterol) that uses fewer samples than the initial certification protocol. This protocol can be applied to analytical systems, reagents, and calibrators that have been previously certified and have not been modified in any way. New and modified products must first be certified through the initial certification protocol.

Must my company recertify before the previous certificate expires?

The list of certified manufacturers is updated monthly. To remain on the list, a manufacturer should anticipate when the certificate expires and plan to repeat the certification. If the certification is not complete, the manufacturer's name will not appear on the monthly update.

My company has problems getting samples of the wide concentration range specified in the protocol. What I can do?

The protocol is designed to cover the concentration range expected for the population. Manufacturers have two options available when some ranges are difficult to cover. First, the manufacturer can arrange with a local clinical laboratory or lipid research clinic to obtain samples (as long as privacy regulations are followed). Second, the manufacturer can arrange with the CRMLN laboratory to provide samples (as long as the samples are fresh when analyzed by the manufacturer's test method). When CRMLN laboratories provide samples, the manufacturer will incur an additional charge.

Is the freshness limit of the samples truly critical?

Yes. One of the primary reasons the CRMLN was established is that freezing, lyophilization, and other processes result in matrix effects that lead to such samples behaving differently from fresh patient samples. The CRMLN protocol, which calls for analysis of fresh samples by the manufacturer's test method, is designed to allow manufacturers to verify their calibration so they obtain the correct result for patient samples. For total cholesterol, the levels of cholesterol in freshly collected samples probably do not change for several days. However, some small studies and anecdotal information indicate that HDL cholesterol and LDL cholesterol change upon storage, so the freshness guidelines are critical (for both the test methods and for the reference methods). The CRMLN has devised a "Sample Stability Protocol" to assist manufacturers in evaluating the stability of frozen samples over time. A copy of the protocol is available on this Web site.

What is the best way to verify that my company's analytical system has low bias before embarking on a full certification effort?

The best way is to perform a comparison with a CRMLN laboratory using six to 10 fresh samples. Another way is to analyze National Institute of Standards and Technology (NIST) SRM 1951b (Lipids in Frozen Human Serum) that was prepared using NCCLS protocol C37-A to minimize matrix effects.

Should my company send in my standards or calibrators to be analyzed by the reference method first?

No. It is not recommended that you send your standards to be analyzed by the reference methods because of matrix differences between fresh samples and calibrators.

Can CDC or the CRMLN lab send my company samples with assigned values to check out my method first?

At this time, neither the CDC nor the CRMLN can provide samples with assigned values.

If my company's among-run QC during the period certification samples were analyzed includes some out-of-control values, can I simply eliminate the out-of-control values if the runs do not include any certification samples i.e., as long as I have a total of 20 runs?

If you have out-of-control runs during the certification process, then you should investigate reasons for the deviation before you re-analyze certification samples (or collection of a new set, depending on the time lapse). Out-of-control runs should not be reported.

Can we perform more than one run on the same day if each test run includes separate calibration and controls?

Yes. CRMLN uses the NCCLS definition of "run" and requires that runs be separated by 2 hours.

Can we use more than one instrument of the same model in the comparison with the CRMLN lab?

Yes, more than one instrument may be used as long as they are different serial numbers from the same model. In this way, manufacturers may increase the number of runs that can be accomplished within a time period. However, different models must perform all of the analyses and be certified separately.

My company manufactures point-of-care (POC) instruments that are factory-calibrated. Are we required to define our runs the same way as traditional clinical analyzers?

Yes. A run for POC instruments is defined as analysis of two samples in duplicate every two hours.

Contact Us:
  • Centers for Disease Control and Prevention
    1600 Clifton Rd
    Atlanta, GA
    30329-4027 USA
  • 800-CDC-INFO
    TTY: (888) 232-6348
  • Contact CDC–INFO The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO
A-Z Index
  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #